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C1.1 The fundamental ideas in chemistry
Atoms and elements are the building blocks of chemistry. Atoms contain protons,
neutrons and electrons. When elements react they produce compounds.
C1.1.1 Atoms
a) All substances are made of atoms. A substance that is made of only one sort of
atom is called an element. There are about 100 different elements. Elements are
shown in the periodic table. The groups contain elements with similar properties.
Candidates should understand where metals and non-metals appear in the periodic
table.
b) Atoms of each element are represented by a chemical symbol, e.g. O represents
an atom of oxygen, and Na represents an atom of sodium.
Knowledge of the chemical symbols for elements other than those named in the
specification is not required.
c) Atoms have a small central nucleus, which is made up of protons and neutrons
and around which there are electrons.
d) The relative electrical charges are as shown:
Name of particle Charge
Proton
+1
Neutron
0
Electron
-1
e) In an atom, the number of electrons is equal to the number of protons in the
nucleus. Atoms have no overall electrical charge.
f) All atoms of a particular element have the same number of protons. Atoms of
different elements have different numbers of protons.
g) The number of protons in an atom of an element is its atomic number. The sum of
the protons and neutrons in an atom is its mass number.
Candidates will be expected to calculate the number of each sub-atomic particle in
an atom from its atomic number and mass number.
h) Electrons occupy particular energy levels. Each electron in an atom is at a
particular energy level (in a particular shell). The electrons in an atom occupy the
lowest available energy levels (innermost available shells). Candidates may answer
questions in terms of either energy levels or shells.
Candidates should be able to represent the electronic structure of the first twenty
elements of the periodic table in the following forms:
Sodium
2,8,1 and diagram
C1.1.2 The periodic table
a) Elements in the same group in the periodic table have the same number of
electrons in their highest energy level (outer electrons) and this gives them similar
chemical properties.
Knowledge is limited to the reactions of Group 1 elements with water and oxygen.
Candidates are not required to know of trends within each group in the periodic
table, but should be aware of similarities between the elements within a group.
b) The elements in Group 0 of the periodic table are called the noble gases. They are
un-reactive because their atoms have stable arrangements of electrons.
Candidates should know that the noble gases have eight electrons in their outer
energy level, except for helium, which has only two electrons.
C1.1.3 Chemical reactions
a) When elements react, their atoms join with other atoms to form compounds. This
involves giving, taking or sharing electrons to form ions or molecules. Compounds
formed from metals and non-metals consist of ions. Compounds formed from nonmetals consist of molecules. In molecules the atoms are held together by covalent
bonds.
Further details of the types of bonding are not required.
Candidates should know that metals lose electrons to form positive ions, whereas
non-metals gain electrons to form negative ions. Knowledge of such transfers is
limited to single electrons.
b) Chemical reactions can be represented by word equations or by symbol
equations. Candidates should be able to write word equations for reactions in the
specification. The ability to interpret given symbol equations in terms of numbers of
atoms is required.
Higher tier candidates should be able to balance symbol equations.
c) No atoms are lost or made during a chemical reaction so the mass of the products
equals the mass of the reactants.
Knowledge and understanding of masses in chemical reactions is limited to
conservation of mass. Calculations based on relative atomic masses are not required
but candidates should be able to calculate the mass of a reactant or product from
information about the masses of the other reactants and products in the reaction.
Suggested ideas for practical work to develop skills and understanding include the
following:
 modelling of atoms (using physical models or computer simulations) to
illustrate chemical reactions at the atomic level
 precipitation reactions, such as lead nitrate with potassium iodide, to show
conservation of mass.